I would agree with that video for official valve servers or servers with no rules, but skial is meant for people who just want to play the game and there are rules against being friendly. That being said, on non skial servers you can kill who you want even if the server goes friendly. That video makes it seem like "its the rules" or "its meanie to kill when everyone is friendly" but at the end of the day people acting friendly are doing so in a game where the goal of the game is to do the objective and that means killing the other team. People can justify it as much as they want, but tf2 is a shooter and thus being killed is part of the game.